As integrated circuit device geometries continue to shrink, manufactures have increasingly turned to optical techniques to perform non-destructive inspection and analysis of semiconductor wafers. Techniques of this type, known generally as optical metrology and inspection, operate by focusing an optical beam from a tool on a portion of a sample and then analyzing the reflected or scattered energy. A higher level of throughput optical system is required in semiconductor manufacture.
The existing optical metrology and inspection methods require about 150 milliseconds for focusing after positioning the tool over a target. Throughput improvement of the existing methods with single head tools puts high demands on different system components. Methods for throughput improvement in an optical inspection system with a single head include shorter move time, shorter target acquisition time and quicker target measurement time. In addition, wafer inspection strategies for design rules smaller than 45 nanometers require a significant increase in the number of measurements per die and per wafer. However, the existing methods cannot provide the desired step function improvement.
It is within this context that the embodiments of the present invention arise.